Field of the Invention
The present invention relates generally to an apparatus for preparing output data for reproducing images on a suitable output or reproduction medium according to an input image data representative of picture elements corresponding to image dots. More particularly, the present invention is concerned with a technique for reducing the required time for preparing such output data from the received input image data.
Discussion of the Prior Art
An output data preparing apparatus as indicated above is generally provided between a data input device and an image output device. A desired image consisting of a plurality or multiplicity of picture elements as superposed on an input coordinate system is entered through the data input device, while an output image corresponding to the input image is reproduced on a suitable output medium such as a recording medium or a display screen. The output image also consists of a multiplicity of output picture elements or image dots as superposed on an output coordinate system. The data input device includes an image input portion such as an image scanner or data entry keyboard, and an image processing portion such as a host computer. For example, the host computer is adapted to define the positions of the input picture elements in the input coordinate system. The image output device may be a laser printer or a CRT display, for example, which includes an image reproducing portion for forming the image dots at the selected picture elements (hereinafter referred to as "output picture elements" where appropriate) on the output medium, and a control portion for controlling the image reproducing portion. Usually, the control portion functions as an apparatus for preparing output data such as printing data in the form of dot data representative of the image dots or output picture elements.
The input coordinate system may be a rectangular coordinate system having mutually perpendicular x and y axes, as shown in FIG. 11A, and picture elements are defined by pixel lines parallel to these x and Y axes. By entering image data through the data input device, the appropriate picture elements as defined in the input coordinate system are selected as the input picture elements at which image dots are to be formed to define an input image. On the other hand, the output coordinate system may be a rectangular coordinate system having mutually perpendicular X and Y axes, as shown in FIG. 11B. As in the input coordinate system, picture elements are defined by pixel lines parallel to the X and Y axes. Image dots are printed at the positions of the specified picture elements as defined in the output coordinate system. These picture elements will be referred to as "output picture elements" where appropriate.
The input coordinate system used by a host computer or other data input device is not always identical with the output coordinate system used by a laser printer, CRT display or other image output device. Although the input and output coordinate systems are both rectangular coordinate systems, these systems often differ in the size of the picture elements, i.e., the image dot size. In the example of FIGS. 11A and 11B, the number of picture elements per unit area of the output coordinate system is larger than that of the input coordinate system. In other words, one input picture element does not necessarily correspond to one output picture element, and often corresponds to a plurality of output picture elements (image dots to be formed). In this case, the number and positions of the output picture elements should be determined for each of the input picture elements of the input image received from the data input device.
In view of the above, a known output data preparing device usually includes outline data preparing means and output data preparing means. The outline data preparing means is adapted to prepare outline data representative of the outline of each output image segment corresponding to each input picture element. The output data preparing means is adapted to prepare output data in the form of dot data representative of the positions of the output picture elements which lie within the outline defined by the prepared outline data, so as to meet a predetermined rule. For instance, the predetermined rule requires that the entire area of each output picture element be located within the outline, or at least a portion of the area of the output picture element be within the outline. An alternative rule requires that the center of each output picture element be located within the outline.
A conventional manner of preparing output dot data from an input image data will be described by reference to FIGS. 11A and 11B. In the example of these figures, the input image is a square defined by four coordinate points P, P1, P2 and P3 in the input coordinate system, namely, a square image consisting of four input picture elements E11, E12, E21 and E22 which are adjacent to each other, as shown in FIG. 11A. On the other hand, the output image (entire output image) corresponding to the input image is obtained by so-called "affine transformation of the coordinates of the input image in the input coordinate system into corresponding coordinates in the output coordinate system according to a predetermined rule, that is, by expanding and transforming the square outline of the input image along a diagonal line which extends from the origin (0, 0) of the input coordinate system, so that the obtained output image is a rhombic image whose four sides are defined by coordinate points P', P1', P2' and P3' in the output coordinate system, as indicated in FIG. 11B. This rhombic output image consists of four segments (output image segments) E11', E12', E21' and E22' which are adjacent to each other.
Taking the output image segment E11', for example, the x and y coordinate values of four points P, Q, R and S defining the corresponding input picture element E11 are converted by the affine transformation into the X and Y coordinate values of four points P', Q', R' and S' defining the output image segment E11'. In this example, the X and Y coordinate values of the four points or apexes P', Q', R' and S' constitute the outline data of the output image segment E11'. Thus, the outline data is prepared for each of the output image segments E11', E12', E21' and E11', and the output picture elements which lie within the outline defined by the outline data are selected for each output image segment. The dot data representative of these selected output picture elements are prepared for each output image segment.
Where the input image is comparatively simple in shape as in the example of FIG. 11A, the X and Y coordinates of the four points P', P1', P2' and P3' defining the entire output image corresponding to the input image may be calculated by the affine transformation of the x and y coordinates of the points P, P1, P2 and P3 of the input image. In this case, the output picture elements which lie within the outline defined by the points P', P1', P2' and P3' are selected so that the output dot data for the entire output image consisting of the selected output picture elements are prepared at one time, without sequentially preparing the sets of dot data for the individual segments E11', E12', E21' and E22'.
However, the input images are not always or necessarily simple in configuration, but are relatively complicated in most cases. Accordingly, the preparation of the dot data corresponding to a complicated input image requires the sequential preparation of sets of dot data for individual segments of the corresponding output image.